A particle beam irradiation apparatus making an actual dose distribution consistent to a planned dose distribution to provide the inside of a target volume with a uniform dose distribution is disclosed in JP-A-2009-66106 (PTL 1) which is characterized by including: a beam generation unit for generating particle beams; a beam extraction control unit for controlling extraction of the particle beams; abeam scan command unit sequentially and two-dimensionally commanding positions of the particle beams to scan slices, which are formed by dividing the target volume to be irradiated along an axial direction of the particle beams, along predetermined trace patterns set in the slices; and a beam scan unit for two-directionally scanning the slices with the particle beams based on the command signal from the beam scan command unit, wherein, after scanning the trace pattern along a forward direction, the beam scan command unit commands the scan positions for scanning the trace patterns along an inverse direction.